1. The Field of the Invention
The present invention is related to infrared tracer compositions which are capable of producing a consistent infrared output when fired from a rifle or other weapon or launch system. More particularly, the present invention relates to infrared tracer compositions which burn reliably and do not require additional igniters for initiation.
2. Technical Background
Tracers bullets and other projectiles are often used in combat and training situations. Tracer bullets provide a visual trace of the path of a projectile. They also provide a relatively reliable means of gauging whether the projectiles fired are impacting upon the desired target or whether adjustments in aim are required.
One of the problems with the use of tracer bullets which emit visible light is that the location of the source of the trace bullet is also discernable. Thus, it is possible for an enemy to visually locate the source of the tracer bullet and to direct a counter-attack toward that location.
For this reason, there has been great interest in the development of tracers that are not visible to the naked human eye. With the development of infrared detection systems, such as night vision goggles, there has been interest in developing tracers which emit infrared light, but which emit little or no visible light. At the same time, it is necessary to tailor the infrared emission such that it is not overly intense at any particular point because very high intensity infrared light could temporarily blind an observer using an infrared detection system.
As early as the 1940's, the United States Army was at work developing "dim" tracer formulations. Dim tracer formulations were generally formulations which gave off only limited visible light, but which emitted significant infrared light. One early formulation designated by the Army as I-136 generally comprised 90.0% strontium peroxide, 10% calcium resonate, and up to about 6.0% magnesium. This formulation, however, had a number of limitations in terms of performance and output.
Eventually the United States Army developed an improved dim tracer formulation designated R-440. This composition is generally comprised of about 40% strontium peroxide, 40% barium peroxide, 10% calcium resinate, and 10% magnesium carbonate.
While R-440 was an improvement over the existing art at the time, the composition presents a number of limitations. For example, the formulation suffers from unreliable ignition. This requires the use of an igniter or an ignition composition associated with the R-440 composition. The ignition composition adds to the complexity and cost of manufacture, and also tends to produce additional visible light during the firing of the tracer.
An addition problem is that R-440 provides a smaller than ideal infrared light output. The composition has a relatively low level near infrared intensity which limits the visibility of the tracer at extended ranges. That is, as the tracer travels closer to the target, the infrared output tends to diminish.
A further problem with R-440 is that the material is a powder. Several problems arise when processing an energetic material in powdered form. It is sometimes observed, for example, that as much as 40% of the material is lost during processing. This is clearly a huge drawback to the use of R-440 and results in a substantial increase in the cost of the product. Furthermore, the small particle size produced by the use of calcium resonate as a binder presents a safety concern. The small powdery particles of the material provide large amounts of surface area which make the material more prone to accidental ignition.
It is desirable in many contexts to provide a tracer that is not only "dim" but which is also "covert." That is, rather than emitting small amounts of visible light, the tracer is essentially free of visible emissions. Convert tracers operate in the same general manner as conventional red, green, and white visible tracers, except that covert tracers produce no visible signature. The achievement completely covert performance has been difficult with conventional formulations.
Accordingly, it would be a substantial advancement in the art to provide covert tracer compositions which overcame some of the problems encountered in the art. It would be an advancement in the art to provide tracer compositions which did not require igniters or ignition compositions in order to operate. It would be a further advancement in the art to provide tracer compositions which had augmented near infrared intensity when compared with conventional compositions. It would be an additional advancement in the art to provide compositions which were not in powder form and which avoided the use of hazardous compositions, such as ozone depleting solvents. It would also be an advancement in the art to provide covert tracer compositions which were safer to use and less sensitive to accidental ignition than conventional tracer compositions.
Such compositions are disclosed and claimed herein.